Step 1: Preheat the Oven. Begin by preheating your oven to 350°F (175°C). This will ensure your bars bake evenly.
Step 2: Prepare the Baking Pan. Grease a 9x13-inch baking pan with a little butter or line it with parchment paper for easy removal later.
Step 3: Mix the Dry Ingredients. In a medium bowl, whisk together the whole wheat flour, all-purpose flour, baking soda, and salt. Set aside.
Step 4: Cream Butter and Sugar. In a large mixing bowl, beat the softened unsalted butter and brown sugar together until light and fluffy. This should take about 2-3 minutes with an electric mixer.
Step 5: Add Peanut Butter, Egg, and Vanilla. Mix in the creamy peanut butter, followed by the egg and 1 teaspoon of vanilla extract. Continue to beat until well combined.
Step 6: Combine Wet and Dry Ingredients. Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Be careful not to overmix!
Step 7: Stir in the Oats. Fold in the old-fashioned oats with a spatula until evenly distributed throughout the batter.
Step 8: Bake the Bars. Spread the batter evenly into the prepared baking pan. Bake in the preheated oven for 20-25 minutes, or until a toothpick inserted in the center comes out clean. Allow the bars to cool completely in the pan on a wire rack.
Step 9: Make the Chocolate Frosting. In a mixing bowl, combine the softened butter, cocoa powder, powdered sugar, milk, and 1 teaspoon of vanilla extract. Beat until smooth and creamy.
Step 10: Frost the Bars. Once the bars are completely cooled, spread the chocolate frosting evenly over the top using a spatula.
Step 11: Cut and Serve. Cut the bars into squares or rectangles and serve. Enjoy your delicious Peanut Butter Oatmeal Bars with Chocolate Frosting!
